For example, consider "Stars Over Salzburg," one of this year's top-rated images. Your first impulse is to marvel at the golden glow of the Austrian city, as seen from an Alpine vantage point high above.

"But then you realize the photographer has moved away from the city to the mountaintops in order to separate himself from the light pollution," Tafreshi, founder of The World at Night, told NBC News in an email. "Inside the yellow light cast by the city, people are no longer able to see this beauty."

"That shows that the lights are shining upward," he said. "Light pollution is not the lights we need for our modern world. It's the unnecessary, wrong-directed and excessive light that scatters to the sky instead of illuminating the ground. It isn't just an astronomer's problem. It's a major waste of energy, it disrupts ecosystems and has adverse health effects."

"Our images try to show how the night sky is an essential part of our environment, and not just an astronomer's laboratory," Tafreshi said. "They display how the night sky is becoming a forgotten part of nature for many people in urban, light-polluted areas. A major goal for us in TWAN imaging is to reclaim the beauties of the night sky and make people aware of this."

The World at Night isn't just about the dark side of the disappearing sky. The winning photos include views that reveal cosmic glories in all their purity. "A good example in this year's contest is 'Crossed Destiny' by Luc Perrot, from Reunion Island near Madagascar," Tafreshi said. "The stunning view of the Milky Way above the Indian Ocean has no touch of our modern world. The galactic band is merged with the horizon of our planet."